updates to accounts_password_pam_dcredit

- Updates XCCDF/OVAL to accounts_password_pam_dcredit from accounts_password_pam_cracklib_dcredit
- Updated OVAL naming schemes (e.g. variable name)
- Updated OVAL to reflect RHEL7
- Updated XCCDF to reflect pam_pwquality not pam_cracklib
Merge pull request #264 from shawndwells/accounts_password_pam_dcredit

OVAL updates for accounts_password_pam_dcredit