tests: make the 'test_pause' helper work in non-verbose mode

tests: make the 'test_pause' helper work in non-verbose mode

When the 'test_pause' helper function invokes the shell mid-test, it
explicitly redirects the shell's stdout and stderr to file descriptors
3 and 4, which are the stdout and stderr of the tests (i.e. where they
would be connected anyway without those redirections).  These file
descriptors are only attached to the terminal in verbose mode, hence
the restriction of 'test_pause' to work only with '-v'.

Redirect the shell's stdout and stderr to the test environment's
original stdout and stderr, allowing it to work properly even in
non-verbose mode, and the restriction can be lifted.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>