Move 'find_dist_version' into utils and use for curl call

EL 5 ships with a uselessly old ca certs bundle that makes it impossible to use
for verifying ssl in curling, which curl does by default. This commit uses the
  find_dist_version method to pass the no verification flag to curl if we're
  building on el5, which some of our acceptance hosts happen to be in jenkins.
  This commit also renames the method to 'el_version', and makes it more
  general purpose.

Signed-off-by: Moses Mendoza <moses@puppetlabs.com>