Reduce JavaFX failure output

[olivierdagenais]

Manual Testing

These steps were performed on my Windows 10 workstation:

1. Temporarily disable the insecure store file to force authentication. I did that by appending .old to %LOCALAPPDATA%/git-credential-manager/insecureStore.xml.

2. Create a file called input.txt containing the following:

   protocol=https
   host=mseng.visualstudio.com
   

3. Launch the GCM4ML in get mode, with stdin coming from input.txt and using a JRE that doesn't support JavaFX, such as Java 6. This is what my command-line looked like:

   /cygdrive/e/Software/Java/jdk1.6.0_20/bin/java -Ddebug=true -jar target/git-credential-manager-1.7.2-SNAPSHOT.jar get < input.txt
   

4. Before the changes from this pull request, we would have gotten the following debug output:

   VsoAadAuthentication::interactiveLogon
   AzureAuthority::acquireToken
   Authorization code could not be obtained: java.lang.IllegalStateException: I don't support your platform yet.
   Unmet requirements for the 'JavaFx' provider:
    - Oracle Java SE 7 update 6 or higher, Oracle Java SE 8, OR OpenJDK 8.
    - JavaFX or OpenJFX runtime JAR.
   
   Please send details about your operating system version, Java version, 32- vs. 64-bit, etc.
   The following System Properties and Environment Variables would be very useful.
   # --- BEGIN SYSTEM PROPERTIES ---
   (...snip...)
   # ---- END SYSTEM PROPERTIES ----
   
   # --- BEGIN ENVIRONMENT VARIABLES ---
   (...snip...)
   # ---- END ENVIRONMENT VARIABLES ----
   
      token acquisition failed.
      interactive logon failed
   VsoAadAuthentication::deviceLogon
   AzureAuthority::acquireToken
   

   ...and now we get the following debug output:

   VsoAadAuthentication::interactiveLogon
   AzureAuthority::acquireToken
   
   Unmet requirements for the 'JavaFx' provider:
    - Oracle Java SE 7 update 6 or higher, Oracle Java SE 8, OR OpenJDK 8.
    - JavaFX or OpenJFX runtime JAR.
   
      token acquisition failed.
      interactive logon failed
   VsoAadAuthentication::deviceLogon
   AzureAuthority::acquireToken
   

5. Re-enable the insecure store file.

Mission accomplished!