[BugFix] [Enhancement] [RHEL/6] Various no{dev,exec,suid} removable partition rules' fixes

This proposal does the following:
* patch 1:
   * fix the mountopt_nodev_on_removable_partitions rule to reference proper external variable (not to result with 'error' on scan)
   * also unify XCCDF id with OVAL id
* patch 2:
  * fix the mountopt_nosuid_on_removable_partitions rule to reference proper external variable (not to result with 'error' on scan)
  * also unify XCCDF id with OVAL id
* patch 3 (mount_option_nodev_removable_partitions rule):
* patch 4 (mount_option_noexec_removable_partitions rule):
* patch 5 (mount_option_nosuid_removable_partitions rule):
   * enhance the corresponding OVAL check to actually test if expected removable partition / device actually exists on the system where the scan is performed (Target Of Evaluation). Since the default value of ```var_removable_partition``` variable is ```/dev/cdrom``` and since there might exists RHEL-6 OS installations without IDE CDROM drive, these checks shouldn't fail when ```/dev/cdrom``` device (or any other removable device defined via ```var_removable_partition```) isn't present on the system, since in that case the OVAL check can't PASS (there's nothing to check ```nodev, noexec``` or ```nosuid``` presence at).

No change has been made to the case when particular removable partition / device is present on the system (IOW it will still FAIL when configured improperly).

Testing report:
--
The proposed change has been tested on both (32-bit & 64-bit) RHEL-6 versions & works as expected (in both cases - expected removable device is present / isn't present on such a system).

Please review.

Thank you, Jan.