Updated installed_OS regex

Slashes in old regex were escaping the ".", making it literally interpretted.
Merge remote-tracking branch 'origin/master' into accounts_password_pam_cracklib_retry

merge for PR 246
Merge branch 'accounts_password_pam_cracklib_retry' of https://github.com/shawndwells/scap-security-guide into shawndwells-accounts_password_pam_cracklib_retry

Conflicts:
	shared/oval/installed_OS_is_rhel7.xml
Merge pull request #259 from shawndwells/installed_OS_regex

Updated installed_OS regex
Merge branch 'shawndwells-accounts_password_pam_cracklib_retry'

Merging installed_OS checks
Merge remote-tracking branch 'upstream/master'