Update 650_check_iso_recoverable.sh

[hpannenb]

Pull Request Details:

• Type: Bug Fix

• Impact: Low

• Reference to related issue (URL):
  NSRSERVER is missing #2162

• How was this pull request tested?
  see NSRSERVER is missing #2162 (comment)

• Brief description of the changes in this pull request:
  Removed the (unnecessary) line in the code of 650_check_iso_recoverable.sh which prevents manually setting the NSRSERVER variable in i.e. local.conf

[jsmeix]

I know nothing about NSR so I blindly trust @hpannenb

[jsmeix]

@hpannenb
thank you for your continuous improvements
of the NSR related code in ReaR!

@rear/contributors
if there are no objections from other ReaR maintainers
I would like to merge it tomorrow afternoon.

[jsmeix]

@hpannenb
FYI regarding setting a variable to a default/fallback value
unless the user had it already set, you may have a look at
how I try to achieve that in default.conf via

test "$VAR" || VAR="default_value"

for example see
https://github.com/rear/rear/blob/master/usr/share/rear/conf/default.conf#L226