Fix build warnings, warnings about Travis Configuration and stalled builds at Travis CI

[tpiekarski]

• Fix Travis stalls build when it comes down to testing lkm_mev (local run works)
• Fix Build Warnings
  warning: ISO C90 forbids mixed declarations and code [-Wdeclaration-after-statement]
• Fix following warnings/issues in .travis.yml
  • root: duplicate key: install
  • root: deprecated key sudo (The key sudo has no effect anymore.)

[tpiekarski]

Last broken build: https://travis-ci.org/github/tpiekarski/lkm-sandbox/builds/681515581
Last working build: https://travis-ci.org/github/tpiekarski/lkm-sandbox/builds/676207146

[tpiekarski]

Build is stalled when both targets test-module name=lkm_mev and test-mev are run.
Reason is so far unknown. It seems not to be a side effect of other targets and also not because
multiple test targets and their modules allocating major number 241.

Following output is logged before the build is continued up to 10 Minutes and then terminated.

make[1]: Entering directory '/home/travis/build/tpiekarski/lkm-sandbox'
Testing module 'lkm_mev' by loading and displaying Kernel Message Ring Buffer
Root permissions are needed for clearing buffer with dmesg and loading/unloading with insmod/rmmod
Testing if the module lkm_mev exists.
Loading module lkm_mev
Testing if module lkm_mev was loaded.