Move the task handling code into the SSTATE_PKGNAME variable using a temporary variable.
This makes the code more understandable as as well as allowing the length of the
final sstate filename to be more easily accesses for following patches.
(From OE-Core rev: be603dad6817948cfa09621d2311046631ec4ab2)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>