build, toaster: record proper task type

build, toaster: record proper task type

Bitbake tasks may be of type 'python' or 'shell',
or they may not be executed at all, which is record
as task type 'noexec'.

In order to record proper task type, this patch:

* creates no exec task type as the default value in
the toaster model definition

* adds full task flags to the bb.build.TaskStarted event
in build.py

* if the task actually starts, the toaster ui will
record the type of the task as either 'python' or 'shell'
based on the task flags.

[YOCTO #5073]
[YOCTO #5075]
[YOCTO #5327]

Signed-off-by: Alexandru DAMIAN <alexandru.damian@intel.com>
Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>