t7001-mv.sh: modernizing test script using functions

t7001-mv.sh: modernizing test script using functions

Test script to verify the presence/absence of files, paths, directories,
symlinks and other features in 'git mv' command are using the command
format:

'test (-e|f|d|h|...)'

Replace them with helper functions of format:

'test_path_is_*'

Replacing idiomatic helper functions:

'! test_path_is_*'

with

'test_path_is_missing'

This uses values of 'test_path_bar' in place of '! test_path_foo' to
bring in the helpful factor of indicating the failure of tests after the
mv command has been used, that is, it echoes if the feature/test_path
exists.

Signed-off-by: Debra Obondo <debraobondo@gmail.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>