Investigate rescue system/shell options for Rockstor

[Hooverdan96]

Putting a placeholder issue here to track possible options for rescue shell/system as was available in the CentOS based installer. One use case is discussed here, relating to root password reset:

rockstor/rockstor-doc#404

Some Possible Options I can think of:

1. define manual process in the docs to perform rescue operations using external tools (e.g. OpenSUSE rescue disk)
2. integrate into Rockstor boot media, basically turning it into a rescue disk by itself
3. side-by-side installation on Rockstor OS drive (could be instead/in addition to the install media option)
4. Do nothing, because it's not considered that important and might create more security risks than benefits
5. ...

It will be important to consider that since we are offering Rockstor across a couple of architectures (x86_84, arm64, pi) that we either have an approach that works for all three or, at least, offer additional workaround documentation where the "most automated" version does not work.

[phillxnet]

@Hooverdan96 There does exist a rescue mode under "Advanced options for Rockstor NAS" on an install resulting from our current installer config built using kiwi-ng 10.1.18 using the "Leap15.6.x86_64" profile. Does this not suffice?

[Hooverdan96]

It might be, I did not have to use it yet. It can't seem to be used for root password reset, since it requests the password before dropping to shell. But maybe that can be kept separately since the process for that has now been documented.