README: restructure & format building manual

README: restructure & format building manual

The commands for package managers for both Ubuntu and RHEL weren't
up-to-date. A few packages doesn't exist anymore or missing from the
latest repositories (e.g. liburing-devel, btrfs-progs-devel).
Ubuntu's list missed a few packages listed in RHEL's list. There are
a few repeating steps. The indent of avaliable environment variables
is not clear.

This patch:
- Update package dependencies for Ubuntu/Debian/RHEL/CentOS/Fedora
- Unify list of packages between Ubuntu/Debian and RHEL/CentOS/Fedora
- Add list of tool packages for other FS
- Add links to tools not in the standard repository for RHEL/CentOS
- Drop xfsprogs-qa-devel reference for old systems
- Replace note about EPEL with installation step with link to Fedora
  manual
- Add configuration examples in 'Setup Environment'
- Small clarification details, such as size of the partition and
  KCONFIG_PATH description
- Removal of repeating steps (install administrative tools,
  partitions content)
- Restructuring and formatting of "BUILDING THE FSQA SUITE" section
- Drop IRIXDEV references in variable set up
- Variables in 'Additional setup' divided into groups
- Move fsqa user/group creation and udf_test to 'Setup Environment'
  section

Signed-off-by: Andrey Albershteyn <aalbersh@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>