Set MESOS_NATIVE_LIBRARY in the testing environment.
Set MESOS_NATIVE_LIBRARY in the testing environment.

We want to force our tests (including the Java ones) to use the most
recent version of our library, so we set MESOS_NATIVE_LIBRARY.

Review: https://reviews.apache.org/r/13175

kaysoky/mesos,verizonlabs/mesos,jpeach/mesos,abudnik/mesos,gsantovena/mesos,verizonlabs/mesos,craimbert/mesos,verizonlabs/mesos,Gilbert88/mesos,asamerh4/mesos,andschwa/mesos,dforsyth/mesos,neilconway/mesos,yuquanshan/customizedMesos,neilconway/mesos,zmalik/mesos,dforsyth/mesos,chhsia0/mesos,abudnik/mesos,craimbert/mesos,neilconway/mesos,Gilbert88/mesos,kaysoky/mesos,abudnik/mesos,asamerh4/mesos,neilconway/mesos,reneploetz/mesos,abudnik/mesos,craimbert/mesos,kaysoky/mesos,Aman-Jain-14/customizedMesos,andschwa/mesos,reneploetz/mesos,dforsyth/mesos,andschwa/mesos,reneploetz/mesos,abudnik/mesos,zmalik/mesos,kaysoky/mesos,yuquanshan/customizedMesos,verizonlabs/mesos,neilconway/mesos,gsantovena/mesos,jpeach/mesos,dforsyth/mesos,reneploetz/mesos,craimbert/mesos,asamerh4/mesos,zmalik/mesos,Aman-Jain-14/customizedMesos,gsantovena/mesos,chhsia0/mesos,dforsyth/mesos,jpeach/mesos,chhsia0/mesos,dforsyth/mesos,Gilbert88/mesos,yuquanshan/customizedMesos,chhsia0/mesos,jpeach/mesos,reneploetz/mesos,gsantovena/mesos,yuquanshan/customizedMesos,Aman-Jain-14/customizedMesos,kaysoky/mesos,verizonlabs/mesos,kaysoky/mesos,zmalik/mesos,neilconway/mesos,yuquanshan/customizedMesos,asamerh4/mesos,abudnik/mesos,craimbert/mesos,reneploetz/mesos,zmalik/mesos,Gilbert88/mesos,Aman-Jain-14/customizedMesos,chhsia0/mesos,abudnik/mesos,yuquanshan/customizedMesos,verizonlabs/mesos,jpeach/mesos,andschwa/mesos,craimbert/mesos,Aman-Jain-14/customizedMesos,andschwa/mesos,andschwa/mesos,gsantovena/mesos,chhsia0/mesos,gsantovena/mesos,asamerh4/mesos,chhsia0/mesos,Aman-Jain-14/customizedMesos,yuquanshan/customizedMesos,zmalik/mesos,kaysoky/mesos,reneploetz/mesos,dforsyth/mesos,Aman-Jain-14/customizedMesos,jpeach/mesos,andschwa/mesos,Gilbert88/mesos,zmalik/mesos,asamerh4/mesos,Gilbert88/mesos,asamerh4/mesos,verizonlabs/mesos,gsantovena/mesos,craimbert/mesos,Gilbert88/mesos,neilconway/mesos,jpeach/mesos