install-deps.sh: let FOR_MAKE_CHECK variable take precedence

install-deps.sh: let FOR_MAKE_CHECK variable take precedence

Previously, the FOR_MAKE_CHECK variable could only enable installing
extra (test) dependencies when install-deps.sh was used and it was
ignored if `tty -s` exited true. This change allows FOR_MAKE_CHECK to
take precedence over the tty check and to specify one of true, 1, yes to
enable extra "for make check" deps or false, 0, no to explicitly disable
the extra deps.

Based-on-work-by: Dan Mick <dan.mick@redhat.com>
Signed-off-by: John Mulligan <jmulligan@redhat.com>