check: Add support for sections in config file

check: Add support for sections in config file

This patch add support for sections in the config file. Each section can
contain configuration options in the format

OPTION=value

when one section is processed xfstests will proceed to next section
until all secitons are processed, or an error occur.

The name of the section can consist of alphanumeric characters + '_',
nothing else is allowed. Name of the section is also used to create
results subdirectory for each section. After all the sections are
processed summary of all runs is printed out.

If the config file does not contain sections, or we're not using config
file at all, nothing is changed and xfstests will work the same way as
it used to.

This is very useful for testing file system with different options. Here
is an example of the config file with sections:

[ext4_4k_block_size]
TEST_DEV=/dev/sda
TEST_DIR=/mnt/test
SCRATCH_DEV=/dev/sdb
SCRATCH_MNT=/mnt/test1
MKFS_OPTIONS="-q -F -b4096"
FSTYP=ext4

[ext4_1k_block_size]
MKFS_OPTIONS="-q -F -b1024"

[ext4_nojournal]
MKFS_OPTIONS="-q -F -b4096 -O ^has_journal"

[ext4_discard_ssd]
MKFS_OPTIONS="-q -F -b4096"
TEST_DEV=/dev/sdc
SCRATCH_DEV=/dev/sdd
MOUNT_OPTIONS="-o discard"

Note that once the variable is set it remains set across the sections, so
you do not have to specify all the options in all sections. However one
have to make sure that unwanted options are not set from previous
sections.

Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>