Fix a numer of issues with glibc post-install step

- Only add dependencies on file, glibc and patchelf if we are building
  CMSSW;
- Only execute post-install relocation for CMSSW. There are no binaries
  in CORAL;
- Remove GLIBC_ROOT environment variable. It was used for bash wrappers
  around cmsRun*. Not needed anymore;
- Do not source init.sh for file and patchelf as we install in
  /afs/.cern.ch (write/read) and then relocate to /afs/cern.ch
  (read-only). The paths in init.sh script are relocated, but files are
  not yet present on /afs/cern.ch. Use binaries directly by full path.
- If grep fails (does not find) the post-install scriplet fails. Ignore
  if grep finds nothing.

__Not tested__

Signed-off-by: David Abdurachmanov <David.Abdurachmanov@cern.ch>
Mmm… actually this is not ok, IIRC. file has a magic file which will not be there (or the system one will be used). Can't we just use the system file? We do not care about this not returning the same architecture on linux and macos, since we grep for ELF.