(QENG-760) support for additional disk for vagrant

- if a given vagrant box has a disk_path then either create a new vmdk
  disk or use the provided disk
- defaults to 50 x 1024 bytes if the disk needs to created
Merge pull request #303 from anodelman/vagrant-maint

(QENG-760) support for additional disk for vagrant
(QENG-714) use all junit tags available for beaker xml output

- switch over to nokogiri (cleaner, easier)
- add logs to system-out tag
- add tag for time that each test suite takes to execute
- add property tags for each beaker option
- add empty junit.xsl stylesheet as a placeholder