convert-srcuri.py: use regex to check space in SRC_URI

convert-srcuri.py: use regex to check space in SRC_URI

There may be none, one or more spaces including tab before backslash in
SRC_URI. Use regex to check and update. It helps to avoid malformed uri
such as recipe open-iscsi-user in meta-openstack:

SRC_URI = "git://github.com/open-iscsi/open-iscsi.git;protocol=https  ;branch=master \

And help to check more recipes such as concurrent-ruby in the same
layer:

SRC_URI = "git://github.com/ruby-concurrency/concurrent-ruby.git;protocol=https;tag=v1.1.6\

Signed-off-by: Kai Kang <kai.kang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>