Disable warnings logged by nuprocess library

[mzarnowski]

When running launcher and bloop is not on the PATH we get the following error:

Starting the bsp launcher for bloop...
Jan 15, 2019 12:39:19 PM com.zaxxer.nuprocess.linux.LinuxProcess start
WARNING: Failed to start process
java.io.IOException: error=2, No such file or directory
	at com.zaxxer.nuprocess.internal.LibJava8.Java_java_lang_UNIXProcess_forkAndExec(Native Method)
	at com.zaxxer.nuprocess.linux.LinuxProcess.start(LinuxProcess.java:109)
	at com.zaxxer.nuprocess.linux.LinProcessFactory.createProcess(LinProcessFactory.java:40)
	at com.zaxxer.nuprocess.NuProcessBuilder.start(NuProcessBuilder.java:266)
	at bloop.launcher.core.Shell.runCommand(Shell.scala:87)
	at bloop.launcher.core.Shell.detectBloopInSystemPath(Shell.scala:153)
	at bloop.launcher.LauncherMain.detectServerState(Launcher.scala:232)
	at bloop.launcher.LauncherMain.connectToBloopBspServer(Launcher.scala:159)
	at bloop.launcher.LauncherMain.runLauncher(Launcher.scala:95)
	at bloop.launcher.LauncherMain.cli(Launcher.scala:78)
	at bloop.launcher.LauncherMain.main(Launcher.scala:59)
	at bloop.launcher.Launcher.main(Launcher.scala)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at coursier.bootstrap.Bootstrap.main(Unknown Source)

A bloop installation has been detected either in the PATH or $HOME/.bloop

NuProcess library is using a logger, which always logs warning when it cannot start, but since bloop is reading the result of the command from the exit code, I am wondering how this (small, but annoying) issue could be addressed? Please, suggest/discuss better solution if you have one.

This PR is a simplest fix I could come up with: disabling warnings from NuProcess (the impact analysis is at the end of this message). It gives us more clear output:

Starting the bsp launcher for bloop...
A bloop installation has been detected either in the PATH or $HOME/.bloop

---

Analysis:
NuProcess is inconsistent... most of the time it just swallows the exception, but in three cases it also logs warnings, before doing nothing...

Those warnings are logged when exception happens while:
a) reading stdout/stderr
b) starting process
c) creating pipes - but this cases does not affect launcher, since the exception is actually propagated after being logged

I believe both a) and b) are of low impact, since launcher depends on exit codes anyway

[jvican]

LGTM, that's a good analysis. I'm merging, a release will be done automatically by the CI and the launcher reference page will contain its latest release version.