Mentorship-android: Add additional tests for SignUpActivity

[iofall]

Add additional tests for the SignUpActivity

Describe the solution you'd like
Espresso tests to cover additional test cases for the SignUpActivity Screen

The tests will go here

Acceptance criteria:

• [ ] Connect Android device or open the emulator
• [ ] On terminal type ./gradlew clean build connectedAndroidTest --stacktrace
• [ ] Wait for your test to complete
• [ ] See the complete report ../mentorship-android/app/build/reports/androidTests/connected/index.html and check if this test passed.

[iofall]

@justdvnsh assigning you!

[justdvnsh]

@iofall Cool. Thanks. Also, please can you label this issue as open source hack ? This would help me in the OSH and help me get involved in the community more.

[justdvnsh]

@iofall Done. Created a PR