e2fsprogs: fix ptest error when using usrmerge DISTRO_FEATURES

e2fsprogs: fix ptest error when using usrmerge DISTRO_FEATURES

Because usrmerge DISTRO_FEATURES is uesed,
in test_script and test_one of ptest scripts, SRCDIR has the wrong path.
  SRCDIR=/usr/usr/lib/e2fsprogs/ptest/test
So we should check and modify SRCDIR in test_script and test_one.

It is a backport for
  https://lists.openembedded.org/g/openembedded-core/message/180486
It should be deleted after yocto version up.

SPEC-4753

Signed-off-by: Qiu Tingting <qiutt@fujitsu.com>
Change-Id: Iff23c1db2b39d9e3e924068cf6ea2c5e26b952bf