[shared, RHEL/6, RHEL/7] Fix 'Uninstall net-snmp Package' rule & add a (shared version) of remediation for it.

Bugfixes - There are multiple issues with the current form of 'Unistall net-snmp Package' rule:
* rule ID "uninstall_net-snmp" doesn't follow the "package_net-snmp_removed" template (fixed in XCCDF
  and also in all profiles that were referencing that rule)
* the package check macro speaks about "net-snmpd" instead of 'net-snmp' (fixed)
* RHEL/7 & Fedora packages_removed.csv templates doesn't speak about already present net-snmp
  OVAL check (fixed)

Enhancements:
* modify Fedora XCCDF to start using the (already present) OVAL
* add shared/ version of the remediation & link / start using it from RHEL/{6,7} & Fedora directories
Merge pull request #316 from iankko/shared_rhel6_rhel7_fix_package_net-snmp_removed_remediation

[shared, RHEL/6, RHEL/7] Fix 'Uninstall net-snmp Package' rule & add a (shared version) of remediation for it