Bash 4.3 or newer have the configure option
--enable-direxpand-default
I suggest backporting a small patch, basically
what is under "#if DIRCOMPLETE_EXPAND_DEFAULT"
from bash 4.3 to rhel7  bash. This would make
the behavior identical to rhel6 bash.

  Example of unexpected behavior:

$ sudo su -
# cd
# mkdir fir
# test=/root/fir
# echo $test
/root/fir
# ls $test<press tab>
# ls $test []
<<< Adds a space for next entry >>>
# ls $test/<press tab>
# ls $test/
<<< Nothing happens >>>
# touch $test/tree.txt

<<<Now the problem:>>>

<<<In RHEL 6.8:>>>

# ls $test/<press tab>
# ls /root/fir/tree.txt
<<<Replaces the $test with /root/fir>>>

<<<In RHEL 7.2:>>>

# ls $test/<press tab>
# ls \$test/tree.txt
ls: cannot access $test/tree.txt: No such file or directory
<<<Adds a \ in front of $test>>>


  Toying a bit with it shows other strange behavior,
for example:

# ls '$test'<press tab>
# ls '$test'-bash: unexpected EOF while looking for matching `''
-bash: syntax error: unexpected end of file

or

# ls "$test"/<press tab>
tree.txt
# ls \$test/tree.txt 

it removes quotes and adds the leading backslash.


I believe the change is better done in bash to match
rhel6 behavior, but it could be done in related /etc/skel
files (shopt -s direxpand).
When updating bash, I suggest adding --enable-direxpand-default
to the configure options.