Have MODULES all_modules by default plus needed adaptions for that

[jsmeix]

• Type: Enhancement

• Impact: Low

Hopefully low impact because this change should only
make things work better by default in the recovery system
without really bad side effects.
The somewhat bigger default recovery system should
not be a really bad side effect.

There is one backward incompatible change:
Before the user had to specify in local.conf

MODULES=( "${MODULES[@]}" 'moduleX' 'moduleY' )

to get additional kernel modules included
but now the user must specify

MODULES=( 'moduleX' 'moduleY' )

for that because with "${MODULES[@]}"
the default value all_modules would be kept
which triggers to get all modules included.

• Reference to related issue (URL):
  Have MODULES=( 'all_modules' ) in default.conf #2041

• How was this pull request tested?

By me on my openSUSE Leap 15.0 system with

MODULES=( 'all_modules' )
MODULES=( 'loaded_modules' )
MODULES=( 'no_modules' )
MODULES=( 'hwpoison-inject' 'trusted' )
MODULES=()

and to me things look o.k.

• Brief description of the changes in this pull request:

Now there is in default.conf

MODULES=( 'all_modules' )

which results that some additional adaptions were needed
in build/GNU/Linux/400_copy_modules.sh and conf/GNU/Linux.conf
because now the default value is no longer empty.

[jsmeix]

@rear/contributors
if there are no objections I would like to merge it today afternoon and
if hell breakes loose afterwards I can fix it or even revert it for ReaR 2.5. ;-)

[gdha]

@jsmeix we will see how it goes - thanks for the enhancement.