fetch2: Add module for ClearCase (ccrc://)

BitBake 'Fetch' clearcase implementation
===============================
The clearcase fetcher is used to retrieve files from a ClearCase (http://en.wikipedia.org/wiki/Rational_ClearCase) repository.

Usage in the recipe:

    SRC_URI = "ccrc://cc.example.org/ccrc;vob=/example_vob;module=/example_module"
    SRCREV = "EXAMPLE_CLEARCASE_TAG"
    PV = "${@d.getVar("SRCREV").replace("/", "+")}"

The fetcher uses the rcleartool or cleartool remote client, depending on which one is available.

Supported SRC_URI options are:

- vob
    (required) The name of the clearcase VOB (with prepending "/")

- module
    The module in the selected VOB (with prepending "/")

    The module and vob parameters are combined to create
    the following load rule in the view config spec:
                load <vob><module>

- proto
    http or https

Related variables:

    CCASE_CUSTOM_CONFIG_SPEC
            Write a config spec to this variable in your recipe to use it instead
            of the default config spec generated by this fetcher.
            Please note that the SRCREV loses its functionality if you specify
            this variable. SRCREV is still used to label the archive after a fetch,
            but it doesn't define what's fetched.

User credentials:

    When using cleartool:
            The login of cleartool is handled by the system. No special steps needed.

    When using rcleartool:
            In order to use rcleartool with authenticated users an `rcleartool login` is
            necessary before using the fetcher.

Signed-off-by: Dennis Meier <meier.dennis@siemens.com>
Reviewed-by: Roger Meier <r.meier@siemens.com>
Reviewed-by: Christian Liechti <christian.liechti@siemens.com>
Reviewed-by: Henrique Mendonca <henrique.mendonca@siemens.com>
Reviewed-by: Pascal Bach <pascal.bach@siemens.com>