BF: tolerate errors while parsing fetch lines

[yarikoptic]

At first I thought to provide special treatment to git config lines and
otherwise keep raising uncaught exception, but then decided that it might be
better to loose some progress information than to crash.
Also _get_push_info below is doing similarish catching of all exceptions
(although doesn't even log them).

With this change, log (if enabled and not suppressed) would show

[WARNING] Git informed while fetching: git config pull.rebase false  # merge (the default strategy)

in the case of recently introduced change to the output in the following
git commit :

d18c950a69f3a24e1e3add3d9fc427641f53e12b is the first bad commit
commit d18c950a69f3a24e1e3add3d9fc427641f53e12b
Author: Alex Henrie <[email protected]>
Date:   Mon Mar 9 21:54:20 2020 -0600

	pull: warn if the user didn't say whether to rebase or to merge

	Often novice Git users forget to say "pull --rebase" and end up with an
	unnecessary merge from upstream. What they usually want is either "pull
	--rebase" in the simpler cases, or "pull --ff-only" to update the copy
	of main integration branches, and rebase their work separately. The
	pull.rebase configuration variable exists to help them in the simpler
	cases, but there is no mechanism to make these users aware of it.

	Issue a warning message when no --[no-]rebase option from the command
	line and no pull.rebase configuration variable is given. This will
	inconvenience those who never want to "pull --rebase", who haven't had
	to do anything special, but the cost of the inconvenience is paid only
	once per user, which should be a reasonable cost to help a number of new
	users.

	Signed-off-by: Alex Henrie <[email protected]>
	Signed-off-by: Junio C Hamano <[email protected]>

 builtin/pull.c               | 16 ++++++++++++++++
 t/t5521-pull-options.sh      | 22 +++++++++++-----------
 t/t7601-merge-pull-config.sh | 38 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 65 insertions(+), 11 deletions(-)

Closes #1014

[Byron]

Thanks a lot!
Since this is an issue many users could start seeing soon, I will cut a release right away.