Add Dragnet check, disable one EBURY check, other minor fixes.

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ADDED - Check for Dragnet malware.

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DISABLED - EBURY 3-digit OpenSSH RPM check is now disabled because there are legitimate 3-digit OpenSSH RPMs found in RHEL/CentOS 6.6, and the other EBURY checks should provide sufficient coverage.

Reported by:
  Kyle Pinkley

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UPDATED - Move printing the EBURY/CDORKED predef information into its own sub because we use it in 16 places.  This will make updating the predef text for these checks much easier in the future.

Suggested by:
  Dave Lanning
  Jerry Johnson

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UPDATED - Add note to Percona RPM check that Percona may cause segfaults on restart of Apache with PHP DSO (for the exact same reason as the two other possible problems that are mentioned).

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UPDATED - Ignore two more harmless rpm.versions.d/local.versions files to prevent unnecessarily warning about them.

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