Executables in APEXes have root:shell

Executables under /system/bin are configured as (uid:gid)=(root:shell)
by fs_config.cpp. Therefore, an executable that is moved/copied from
/system/bin to an APEX should be configured as such.

Test: adb shell ls -al /system/bin/linker
/apex/com.android.runtime/bin/linker shows
-rwxr-xr-x 1 root shell 1133528 1970-01-01 09:00 /apex/com.android.runtime/bin/linker
-rwxr-xr-x 1 root shell 1133528 1970-01-01 09:00 /system/bin/linker

Change-Id: Ibb698aab237362fed312da2af809cceead8a1092

apex/apex.go

@@ -40,7 +40,7 @@ var (
 		Command: `echo '/ 1000 1000 0755' > ${out} && ` +
 			`echo '/apex_manifest.json 1000 1000 0644' >> ${out} && ` +
 			`echo ${ro_paths} | tr ' ' '\n' | awk '{print "/"$$1 " 1000 1000 0644"}' >> ${out} && ` +
-			`echo ${exec_paths} | tr ' ' '\n' | awk '{print "/"$$1 " 1000 1000 0755"}' >> ${out}`,
+			`echo ${exec_paths} | tr ' ' '\n' | awk '{print "/"$$1 " 0 2000 0755"}' >> ${out}`,
 		Description: "fs_config ${out}",
 	}, "ro_paths", "exec_paths")