OPENDJ-2177 Set man path in native packages

Set man path in DEB and RPM package.
Check if the man path directive is already present in the man config
file. If so, we do nothing, otherwise we add our opendj man pages path
(/opt/opendj/share/man).
Note that for this step is done at the end of the postinstall phase.
For the DEB script, we needed to remove the 'set -e'to allow grep to
return a non zero code.
Thats why we have enforced upgrade return code checks.