Use [*] instead of [@] for array expansion inside a string

[pcahyna]

Relax-and-Recover (ReaR) Pull Request Template

Please fill in the following items before submitting a new pull request:

Pull Request Details:

• Type: Style Cleanup

• Impact: Low

• Reference to related issue (URL):
  https://github.com/rear/rear/pull/1887/files#r268264260

• How was this pull request tested?
  Code analysis and experimenting with analogous snippets of bash code.

• Brief description of the changes in this pull request:
  Array expansion inside strings like "aaa ${boot_list[@]} bbb" splits the string into several strings:

boot_list=( foo bar )
"aaa ${boot_list[@]} bbb"

-> "aaa foo" "bar bbb" instead of "aaa foo bar bbb". This is probably unintended, although harmless in this case.
Change [@] to a more intuitive [*], which keeps the result of expansion as one string.
See https://github.com/koalaman/shellcheck/wiki/SC2145

[jsmeix]

@rmetrich
I assign this to you because you did #2096
and #2097 before
(and I know nothing about what syntax the bootlist command needs).

[jsmeix]

I agree with https://github.com/rear/rear/pull/1887/files#r268264260

[rmetrich]

There is indeed a diff, but not really seen when echoing:

$ boot_list=( foo bar )

$ for v in "aaa ${boot_list[@]} bbb"; do echo "$v"; done
aaa foo
bar bbb

$ for v in "aaa ${boot_list[*]} bbb"; do echo "$v"; done
aaa foo bar bbb

[jsmeix]

@pcahyna
thank you for your precise inspection of the details is the code!

Because of this I added
#1068 (comment)