sstate.bbclass: fix error handling when sstate mirrors is ro

The commit dd555537fc
'sstate.bbclass: fix errors about read-only sstate mirrors'
adds an additional exception handler to silently mask read
only rootfs errors thrown during the touch.

The exception handler checks the error type with the python module errno
but this module needs to be imported as it don't exist.

Example of the error:

File: 'exec_python_func() autogenerated', lineno: 2, function: <module>
     0001:
 *** 0002:sstate_task_postfunc(d)
     0003:
File: '/home/builder/src/base/poky/meta/classes/sstate.bbclass', lineno: 778, function: sstate_task_postfunc
     0774:
     0775:    omask = os.umask(0o002)
     0776:    if omask != 0o002:
     0777:       bb.note("Using umask 0o002 (not %0o) for sstate packaging" % omask)
 *** 0778:    sstate_package(shared_state, d)
     0779:    os.umask(omask)
     0780:
     0781:    sstateinst = d.getVar("SSTATE_INSTDIR")
     0782:    d.setVar('SSTATE_FIXMEDIR', shared_state['fixmedir'])
File: '/home/builder/src/base/poky/meta/classes/sstate.bbclass', lineno: 708, function: sstate_package
     0704:        except PermissionError:
     0705:            pass
     0706:        except OSError as e:
     0707:            # Handle read-only file systems gracefully
 *** 0708:            if e.errno != errno.EROFS:
     0709:                raise e
     0710:
     0711:    return
     0712:
Exception: NameError: name 'errno' is not defined

(From OE-Core rev: 2e5cf13aa46f25d8976ece55fcb4129bfd75659f)

Signed-off-by: Jose Quaresma <quaresma.jose@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 15f30ad144fbe25e9a5e71bc7e42e746d2039992)
Signed-off-by: Anuj Mittal <anuj.mittal@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/sstate.bbclass

@@ -705,6 +705,7 @@ def sstate_package(ss, d):
             pass
         except OSError as e:
             # Handle read-only file systems gracefully
+            import errno
             if e.errno != errno.EROFS:
                 raise e
 
@@ -1152,6 +1153,7 @@ python sstate_eventhandler() {
                 pass
             except OSError as e:
                 # Handle read-only file systems gracefully
+                import errno
                 if e.errno != errno.EROFS:
                     raise e