libpcp_pmda: close help files after mmap'ing contents
libpcp_pmda: close help files after mmap'ing contents

There have been a number of reports of an selinux AVC where
mdadm (which is run from pmdalinux) is blocked from 'read'
access on /var/lib/pcp/pmdas/linux/help.pag (local context
is also possibly in play).  The help text files are opened
and mapped in pmdaOpenHelp(3) but there is no reason for us
to keep them open after that, propogating the 2 descriptors
across fork/exec for subsequent accidental access by other
utilities like mdadm.

This resolves Fedora BZ 1721644 (and several duplicate BZs).

adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp