recipetool: create: fix SRCBRANCH not being passed to params

When explicitly passing a branch using --srcbranch in 'devtool add' or
'recipetool create', the branch name is not included in the params of
bb.fetch2.encodeurl and default 'master' branch is used instead.

Signed-off-by: Tuomas Salokanto <tuomas.salokanto@gmail.com>
Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>