(SERVER-29) Set JARS_NO_REQUIRE='true' on scripting containers.

JARS_NO_REQUIRE is an environment variable which, if set to `true`, will prevent
the loading of embedded jars using the `require_jar' method of the
`jar-dependencies` gem.

This is required to ensure that jruby-openssel, which is loaded by the JRuby
Kernel whenever ruby code requires 'openssl', does not attempt to load embedded
bouncy castle jars onto the classpath. The effect is to ensure that
jruby-openssl uses the bouncycastle included as a requirement of
jvm-certificate-authority rather than the version included with JRuby, as well
as preventing jvm-ceritificate-authority from using JRuby's bouncycastle.

This commit also adds an integration smoke test to ensure that the jar is
actually excluded by listing the contents of the jar then using the
`assert_no_match` minitest method to validate the listed output does not contain
BC jars.
(MAINT) Fix intermittent gem install failures.

* Change list of installed gems to reduce complexity of install. Beaker changes
  too often to use it here without specifying a concrete version, which in turn
  would require more complex handing of this list of gems throughout the rest of
  the test.
* Clears the list of rubygems sources before adding the internal mirror to
  ensure that gem installation problems are not masked by network failures.
Merge pull request #338 from waynr/maint

(MAINT) Fix intermittent gem install failures.
Merge pull request #331 from waynr/server-29

(SERVER-29) Set JARS_NO_REQUIRE='true' on scripting containers.
(SERVER-29) Fix jruby interpreter test.
Merge pull request #341 from waynr/server-29

(SERVER-29) Fix jruby interpreter test.
(SERVER-259) Improve validate-memory-requirements! error message

Without this patch the error message given to the user when RAM is less
than 1.1 * JVM heap size is the following following:

    Not enough RAM. Puppet Server requires at least 2181MB of RAM.

This is a problem because it leads the user to believe they don't have
enough RAM.  They may conclude their only recourse is to add more memory
when another recourse is to decrease the configured maximum JVM heap
size.

This patch addresses the problem by augmenting the error message to
specifically call out the JVM heap setting as a possible recourse.  The
message further tries to help the user by directing them to the
JAVA_ARGS, -Xms, -Xmx options, and the locations of the configuration
files on Debian and Enterprise Linux, the most common platforms.