Allow to execute postinstall in adb sideload

In recovery, everything is labeled rootfs, including
/system/bin/*. Allow postinstall to execute them in recovery.

Test: sideload
Bug: 116608795
Fixes: 119877813
Change-Id: I5682bdecd0df1cb9ff3bc968ea29449b0b8588f4

public/postinstall.te

@@ -19,6 +19,11 @@ allow postinstall shell_exec:file rx_file_perms;
 allow postinstall system_file:file rx_file_perms;
 allow postinstall toolbox_exec:file rx_file_perms;
 
+# Allow postinstall to execute shell in recovery.
+recovery_only(`
+  allow postinstall rootfs:file rx_file_perms;
+')
+
 #
 # For OTA dexopt.
 #