[CMake] set INSTALL_RPATH for python on linux

To avoid the need to set `LD_LIBRARY_PATH` when the
`CMAKE_INSTALL_PREFIX` is not a standard one.
7 jobs for pr/241 in 10 minutes and 28 seconds (queued for 1 second)
Name Stage Failure
failed
format Test
./unittest/python/test_LDLT.py:14:19: W291 trailing whitespace
./unittest/python/test_LDLT.py:15:19: W291 trailing whitespace
./unittest/python/test_LDLT.py:16:27: W291 trailing whitespace
./unittest/python/test_LDLT.py:18:92: E231 missing whitespace after ','
./benchmarks/bench-switch.py:6:1: F401 'time' imported but unused
./benchmarks/bench-switch.py:7:1: F401 'timeit' imported but unused
./benchmarks/bench-switch.py:53:24: E703 statement ends with a semicolon
Cleaning up file based variables
ERROR: Job failed: exit code 1