<mongodb cart> adapt to use SCL-provided mongodb

Bug 1073126
https://bugzilla.redhat.com/show_bug.cgi?id=1073126

Adds `lib/mongodb_context`, which wraps MongoDB executables with
appropriate SCL context

Adds `update_configuration` function: sets up `PATH`, `MANPATH`, and
`LD_LIBRARY_PATH` for shell env

Update `mongo` shell function in `rhcsh`: don't clear `LD_LIBRARY_PATH`
before calling `mongo`, trust the `PATH` variable to find the right
`mongo`, and resolve `mongo` path into var `mongo_bin`

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mongodb cart: address bugs with scaled carts

Bug 1073126
https://bugzilla.redhat.com/show_bug.cgi?id=1073126#c8

Add `publish-ld-library-path-info` hook, lock `mongodb/lib` directory

Also addresses issue with `rhcsh` where correct `mongo` bin isn't
necessarily on the `PATH`

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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

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 mongodb cart: clean up `mongodb_context`

Integrating Miciah's suggestions to simplify `update_configuration` -
smarter path element generation and more correct handling for empty
`ld_path` variables
That's obviously a much better solution.