Rcov tests

* use ruby version manager instead of system ruby (1.9.3 instead of 1.8.7, do not use sudo, support Rcov generation);
* use dynamic determination of the current bash scrip directory (work in MacOS and FreeBSD also, available to run in subdirectory of jennins workspace).

Example:
https://fuel-jenkins.mirantis.com/job/astute-rspec-check/48/