toaster: add two-stage commit startup logic

Toaster start script lunches multiple process components
of the toaster system.

This patch adds logic into the startup script to
safely fail startup and do proper cleanup on any error
that may happen during system start.

Bitbake needs to return 0 if it will successfully lunches
the server-mode.

Signed-off-by: Alexandru DAMIAN <alexandru.damian@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
bitbake: usermanual.xml: fix a typo

Fixed:
"should created" -> "should be created"

[YOCTO #5703]

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
bitbake/lib/bb/build.py: fix the task flags cleandirs

The user manual said:

'cleandirs' - directories which should created before the task runs but should be empty

But it only removes the dir, doesn't create it

[YOCTO #5703]

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
bitbake: fetch2/git: add nobranch option for SRC_URI to skip SHA validating for branch

For rebased git tree, some commits doesn't exist in any branch, and such commits are
valid in tag, the change is useful for such case.

Signed-off-by: Zhenhua Luo <zhenhua.luo@freescale.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>