RFE: Support kickstart files in rescue mode - take 2

[Alexander Todorov <atodorov redhat com>]

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Hello folks,
I've done some more work on this feature and here's the result:

*) Add rescue command to pykickstart. Synopsis is:
~   rescue [--nomount | --romount]

*) In loader.c - always pass --kickstart <url> to stage 2

*) Add setRescueModeFromKickstart function in anaconda to handle the flag for
rescue mode from command line or kickstart. Similar to 'vnc'.

*) In anaconda process the kickstart file if present and we're going in rescue mode.

*) In rescue.py do:
~  - if nomount then execute %post else;
~  - mount rw by default or read only if kickstart tells us to
~  - write to the log instead of popping up windows
~  - at the end execute %post

What is tested with F9 and works is: boot with the following options on cmd line
and/or kickstart

cmd line       | ks.cfg
- ---------------+--------
~               | rescue
~ rescue        |
~ rescue        | rescue
- ---------------+---------------------> shows that we properly enter rescue mode
rescue nomount |
rescue nomount | rescue
~               | rescue --nomount
- ---------------+---------------------> shows that nomount works properly
~               | rescue --nomount --romount  -----> expected kickstart error
- ---------------+---------------------
~               | rescue --romount
- ---------------+----------------------> shows that read only mount works [1]

[1] - rescue --romount will work only when we have %post --nochroot. Looks like
it first does chroot and then saves the script text under /tmp for execution.
This fails as /tmp is on the chrooted read-only file system. Sounds expected to me.

Thanks,
Alexander.
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