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>