ATest: Change module_name from list to single string.

ATest's original module_name is designed as a single string.
The different type maybe cause some problem when loading module_name
data. Due to it expected it as a list but actually it will be a single
string after mod-info obj handling this data.

Bug: 113317515
Test: atest aapt2_tests
      atest hello_world_test
      atest BluetoothInstrumentationTests
      atest packages/apps/Bluetooth/tests/unit/Android.mk
      atest RunBluetoothRoboTests
      atest com.android.bluetooth
      atest libcore/luni/src/test/java/libcore/javax/net/ssl/SSLSocketTest.java
        Multiple tests found:
	  0: libjavacore-unit-tests
          1: jsr166-tests
          2: core-ojtests-public
	  ...
      atest SSLSocketTest # Brings up 2 prompts, one for which file then one for which module
      make -j bit
      bit Settings
      bit hello_world_test
      bit BluetoothInstrumentationTests
      bit RunBluetoothRoboTests (Could not find module, but the same situation
          before applying this patch)


Change-Id: I46a14c675eabd7cebd82562954380a9a769e80b5