This is required for programs using rocksdb and and typeinfo.

Otherwise, linking them fails with errors like this (that's ceph):

/nix/store/cg0k49h66nkdqx6ccwnqr0i4q0fnfznc-binutils-2.31.1/bin/ld: ../../lib/libos.a(RocksDBStore.cc.o):(.data.rel.ro._ZTIN12RocksDBStore14RocksWBHandlerE[_ZTIN12RocksDBStore14RocksWBHandlerE]+0x10): undefined reference to `typeinfo for rocksdb::WriteBatch::Handler'
/nix/store/cg0k49h66nkdqx6ccwnqr0i4q0fnfznc-binutils-2.31.1/bin/ld: ../../lib/libos.a(RocksDBStore.cc.o):(.data.rel.ro._ZTIN12RocksDBStore19MergeOperatorRouterE[_ZTIN12RocksDBStore19MergeOperatorRouterE]+0x10): undefined reference to `typeinfo for rocksdb::AssociativeMergeOperator'
/nix/store/cg0k49h66nkdqx6ccwnqr0i4q0fnfznc-binutils-2.31.1/bin/ld: ../../lib/libos.a(RocksDBStore.cc.o):(.data.rel.ro._ZTIN12RocksDBStore19MergeOperatorLinkerE[_ZTIN12RocksDBStore19MergeOperatorLinkerE]+0x10): undefined reference to `typeinfo for rocksdb::AssociativeMergeOperator'
/nix/store/cg0k49h66nkdqx6ccwnqr0i4q0fnfznc-binutils-2.31.1/bin/ld: ../../lib/libos.a(RocksDBStore.cc.o):(.data.rel.ro._ZTI17CephRocksdbLogger[_ZTI17CephRocksdbLogger]+0x10): undefined reference to `typeinfo for rocksdb::Logger'
/nix/store/cg0k49h66nkdqx6ccwnqr0i4q0fnfznc-binutils-2.31.1/bin/ld: ../../lib/libos.a(BlueRocksEnv.cc.o):(.data.rel.ro._ZTI12BlueRocksEnv[_ZTI12BlueRocksEnv]+0x10): undefined reference to `typeinfo for rocksdb::EnvWrapper'
/nix/store/cg0k49h66nkdqx6ccwnqr0i4q0fnfznc-binutils-2.31.1/bin/ld: ../../lib/libos.a(BlueRocksEnv.cc.o):(.data.rel.ro._ZTI23BlueRocksSequentialFile[_ZTI23BlueRocksSequentialFile]+0x10): undefined reference to `typeinfo for rocksdb::SequentialFile'
/nix/store/cg0k49h66nkdqx6ccwnqr0i4q0fnfznc-binutils-2.31.1/bin/ld: ../../lib/libos.a(BlueRocksEnv.cc.o):(.data.rel.ro._ZTI25BlueRocksRandomAccessFile[_ZTI25BlueRocksRandomAccessFile]+0x10): undefined reference to `typeinfo for rocksdb::RandomAccessFile'
/nix/store/cg0k49h66nkdqx6ccwnqr0i4q0fnfznc-binutils-2.31.1/bin/ld: ../../lib/libos.a(BlueRocksEnv.cc.o):(.data.rel.ro._ZTI21BlueRocksWritableFile[_ZTI21BlueRocksWritableFile]+0x10): undefined reference to `typeinfo for rocksdb::WritableFile'
/nix/store/cg0k49h66nkdqx6ccwnqr0i4q0fnfznc-binutils-2.31.1/bin/ld: ../../lib/libos.a(BlueRocksEnv.cc.o):(.data.rel.ro._ZTI17BlueRocksFileLock[_ZTI17BlueRocksFileLock]+0x10): undefined reference to `typeinfo for rocksdb::FileLock'

(cherry picked from commit 781d85c)

correct platforms. ceph currently doesn't build on aarch64-linux. So
let's not lie in meta.platforms.

ceph: fix multiple output
We currently just move $out/share/ceph/mgr to
$lib/lib/ceph, and then remove all references to $out with a find
command.

I checked $out, the only reference to $out is in
$lib/lib/ceph/libceph-common.so.0, coming from src/common/options.cc:
https://github.com/ceph/ceph/blob/master/src/common/options.cc#L5050:

>  Option("mgr_module_path", Option::TYPE_STR, Option::LEVEL_ADVANCED)
>  .set_default(CEPH_DATADIR "/mgr")
>  .add_service("mgr")
>  .set_description("Filesystem path to manager modules."),

Just removing the reference might break some behaviour - it should point
to $lib/ceph/mgr instead.

We can fix this in a much more elegant fashion by just passing a custom
CMAKE_INSTALL_DATADIR to the build system.

ceph: fix outdated Boost::python substitutions

Instead of substituting in CMakeLists.txt files, one now needs to set
MGR_PYTHON_VERSION.

ceph: clean up PYTHONPATH wrapping

Set `pythonPath` instead of exporting PYTHONPATH.

Use `toPythonPath` to construct the PYTHONPATH where we need manual
wrapping. There's no ceph-volume, only ceph-mgr.

ceph: set doCheck = false explicitly

and describe why.

ceph: patch more shebangs

ceph: use system-provided gtest and rocksdb
(cherry picked from commit 05590b3)

(cherry picked from commit c373fc3)

(cherry picked from commit fe4d213)

Rename the old ceph test to ceph-single-node and add a new test
ceph-multi-node. The ceph-single-node represents a dev cluster whereas
ceph-multi-node is closer to a prod cluster.

(cherry picked from commit 9165201)

(cherry picked from commit 6ac9d1f)

…ests.nix

(cherry picked from commit 5fbf0cf)