Fix Travis & missing build dependency

[liujed]

• Added missing build dependency. The control plane now depends on the front end, so that the parser is built before the P4Runtime serializer. This fixes a heisenbug in the build process.

• Build now checks for bison>=3.0.2.

• Don't clobber the user's .bash_profile in install_os_deps.sh.

• Fix Travis OS X job. Modifying .bash_profile isn't good enough for Travis. Have to set
  environment variables in .travis.yml.

[mihaibudiu]

I hope this works better... Can't tell.

[liujed]

@mbudiu-vmw: I wasn't able to reproduce your build issue until I did a make -j1. This fixes that particular issue for me. I haven't sat through an entire make -j1 build yet, though.

For posterity, here is the error output showing the build dependency between the control plane and the parser:

[  8%] Building CXX object p4c/control-plane/CMakeFiles/controlplane.dir/unified_controlplane_sources_1.cpp.o                                                   
In file included from /data/bf-p4c-compilers/p4c/frontends/parsers/parserDriver.h:25:0,
                 from /data/bf-p4c-compilers/p4c/frontends/p4/parseAnnotations.h:21,
                 from /data/bf-p4c-compilers/p4c/control-plane/p4RuntimeSerializer.cpp:45,
                 from /data/bf-p4c-compilers/build/p4c/control-plane/unified_controlplane_sources_1.cpp:4:
/data/bf-p4c-compilers/p4c/frontends/parsers/p4/abstractP4Lexer.hpp:4:45: fatal error: frontends/parsers/p4/p4parser.hpp: No such file or directory
 #include "frontends/parsers/p4/p4parser.hpp"
                                             ^
compilation terminated.
p4c/control-plane/CMakeFiles/controlplane.dir/build.make:217: recipe for target 'p4c/control-plane/CMakeFiles/controlplane.dir/unified_controlplane_sources_1.cpp.o' failed
make[3]: *** [p4c/control-plane/CMakeFiles/controlplane.dir/unified_controlplane_sources_1.cpp.o] Error 1
CMakeFiles/Makefile2:2331: recipe for target 'p4c/control-plane/CMakeFiles/controlplane.dir/all' failed
make[2]: *** [p4c/control-plane/CMakeFiles/controlplane.dir/all] Error 2
CMakeFiles/Makefile2:1798: recipe for target 'p4c/extensions/bf-p4c/CMakeFiles/p4c-barefoot.dir/rule' failed
make[1]: *** [p4c/extensions/bf-p4c/CMakeFiles/p4c-barefoot.dir/rule] Error 2
Makefile:743: recipe for target 'p4c-barefoot' failed
make: *** [p4c-barefoot] Error 2

[liujed]

Travis job for OS X seems to be running into #83. @cc10512's theory is that this is caused by a recent OS X update.