Check if jenkins_home/plugins exists

The code was raising an exception if ~jenkins
existed, but ~jenkins/plugins didn't. Change
the code to check for plugins from jenkins_home.
Creting home directory for jenkins user
Updating user home to use default JENKINS_HOME of /var/lib/jenkins instead of /home/jenkins
Merge pull request #73 from dtsato/master

Creating home directory for jenkins user
fix travis ruby 1.8.7 issues
add puppet 3.3, 3.4, remove 3.0 for rspec >= 1
Merge pull request #79 from jlambert121/ruby187

fix travis ruby 1.8.7 issues
lint fix
Add note about plugin dependencies to README.markdown
Merge remote-tracking branch 'upstream/master'
Merge pull request #83 from jchristi/master

Add note about plugin dependencies to README.markdown
Merge pull request #82 from dcrissman/dev

Lint Fix
Merge pull request #68 from ambakshi/fix-jenkins-plugins-facter

Check if jenkins_home/plugins exists
confine fact to only run on linux boxes

Confining this fact required moving the conditional and variables inside the `setcode` block, however the overall logic of the fact is unchanged. This change also includes the recent patch 7c03e35ce4f5d2c7a112142cf58cb714f95dff02

I've tested this on Linux Jenkins box, and on a Windows box and it's working as expected.
Merge pull request #87 from robbyt/patch-1

confine fact to only run on linux boxes
fix typo in init.pp
Merge pull request #88 from UCB-RAC/master

fix typo in init.pp
Change whitespace, indentation or line-breaks
Change variables in template to puppet 3.x way
Merge pull request #71 from kronn/resolve-puppet-warnings

Resolve puppet warnings