mongodb cart: Support non-SCL systems

Bug 1104072
https://bugzilla.redhat.com/show_bug.cgi?id=1104072

This commit updates the cart spec file to conditionally call the
`mkjournal` script with or without SCL mongo, updates `mongodb_context`
to support non-scl mongo and tweaks `rhcsh` in a similar manner.

Additional fixes include:

* modify the `mongo` function in `rhcsh` to properly quote
  user-specified parameters for passing to `scl enable mongodb24`

* conditionally publish path elements so the correct `mongo*` binaries
  are preferred in scaled and non-scaled environments

* defensively quote user-specified parameters in function `mongo` in
  `rhcsh` so that things like exotic passwords that contain spaces are
  passed to the `mongo` binary without being erroneously split into
  multiple arguments