Save cause of download error for BuildException

[jgneff]

When downloading external binaries, save any IOException for the cause parameter of the BuildException. Otherwise, the root cause of the build failure is always null.

[jgneff]

When the build fails to download an external binary because of an IOException, the root cause of the failure is always null. This pull request saves the exception so that it can be reported in the build error message.

Before

Before this change, the error is reported with a null root cause as shown below:

[downloadbinaries] Could not download
EC27...6746-wordlist-en_GB-large-2017.08.24.zip to
/root/.hgexternalcache/EC27...6746-wordlist-en_GB-large-2017.08.24.zip:
/build/.../parts/netbeans/build/nbbuild/build.xml:276:
  Could not download
  EC27...6746-wordlist-en_GB-large-2017.08.24.zip from
  https://netbeans.osuosl.org/binaries/: null

After

After this change, the original IOException is printed as the root cause:

[downloadbinaries] Could not download
EC27...6746-wordlist-en_GB-large-2017.08.24.zip to
/root/.hgexternalcache/EC27...6746-wordlist-en_GB-large-2017.08.24.zip:
/build/.../parts/netbeans/build/nbbuild/build.xml:276:
  Could not download
  EC27...6746-wordlist-en_GB-large-2017.08.24.zip from
  https://netbeans.osuosl.org/binaries/: java.io.IOException:
    Skipping download from
    https://netbeans.osuosl.org/binaries/EC27...6746-wordlist-en_GB-large-2017.08.24.zip
    due to response code 503

Now I see that the HTTPS proxy server in my build environment is returning a response status code of 503 Service Unavailable for this file:

The 503 (Service Unavailable) status code indicates that the server is currently unable to handle the request due to a temporary overload or scheduled maintenance, which will likely be alleviated after some delay.

Tests

I ran the unit tests for the NetBeans Ant task downloadbinaries as follows:

$ ant -Dincludes=**/DownloadBinariesTest.class localtest
  ...
localtest:
    [junit] Testsuite: org.netbeans.nbbuild.extlibs.DownloadBinariesTest
    [junit] Tests run: 4, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.162 sec
    [junit]

BUILD SUCCESSFUL
Total time: 1 second

[vieiro]

Thanks, @jgneff !

[matthiasblaesing]

Thank you - looks good, unittests are green. Lets get this in.