runqemu: fix incorrect calls to get variable values

We were specifying a default parameter; the get() function defined here
does not take such a parameter. I appears this code had not been tested.
This fixes runqemu erroring out immediately when used within the eSDK.

(From OE-Core rev: e4548531112c824653ae42b9bcc335a7ca8588e0)

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

scripts/runqemu

@@ -732,8 +732,8 @@ class BaseConfig(object):
                 # be able to call `bitbake -e`, then try:
                 # - get OE_TMPDIR from environment and guess paths based on it
                 # - get OECORE_NATIVE_SYSROOT from environment (for sdk)
-                tmpdir = self.get('OE_TMPDIR', None)
-                oecore_native_sysroot = self.get('OECORE_NATIVE_SYSROOT', None)
+                tmpdir = self.get('OE_TMPDIR')
+                oecore_native_sysroot = self.get('OECORE_NATIVE_SYSROOT')
                 if tmpdir:
                     logger.info('Setting STAGING_DIR_NATIVE and STAGING_BINDIR_NATIVE relative to OE_TMPDIR (%s)' % tmpdir)
                     hostos, _, _, _, machine = os.uname()