(maint) Use activerecord 2.2.3 on CentOS 5

Without this patch the ENC acceptance test is attempting to install
activerecord 3.0.20 on CentOS 5.  This is a problem because activerecord
3.0.20 requires a more recent version of rubygems than is available in
CentOS 5 resulting in activerecord not being installed.

This patch addresses the problem by using a selector to install an older
version of activerecord on EL 5 systems, allowing the test to pass
successfully.
Merge branch 'fix_activerecord_centos' into stable

* fix_activerecord_centos:
  (maint) Use activerecord 2.2.3 on CentOS 5
Merge branch 'stable'

* stable:
  (maint) Use activerecord 2.2.3 on CentOS 5
add support for an external autosign command

This change adds 2 parameters:

1. `csr_attributes_file`
Allows for specifying user defined attributes to be added to the CSR. The file is yaml instead of flat key/value as this allows you to have an array of values for a parameter (which is also allowed in a CSR).

2. `autosign_command`
Allows for running an external command to determine whether a certificate should be automatically signed or not. The command is passed the certificate name as the first argument. The command should then exit with status `0` to indicate that the certificate should be signed, and status non-0 to indicate it should not be signed.