tests: fix cosmetic permission issues during `make install`

tests: fix cosmetic permission issues during `make install`

files in dist_*_SCRIPTS get installed with 0755, those in dist_*_DATA
with 0644. This commit moves all .kshlib, .shlib and .cfg files in the
testsuite to dist_pkgdata_DATA, and removes the shebang from
zpool_import.kshlib.

This ensures that the files are installed with appropriate permissions
and silences some warnings from lintian

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: loli10K <ezomori.nozomu@gmail.com>
Reviewed by: John Kennedy <john.kennedy@delphix.com>
Signed-off-by: Stoiko Ivanov <s.ivanov@proxmox.com>
Closes #8803