Try to make the internal fboss-oss test better match external build

Summary:
This is hard to do because we don't have root and cannot install
new deps in place on the legocastle machines.  Trying to work with
someone from legocastle team to fix this, but in the mean time, this
might work.

Reviewed By: aeckert

Differential Revision: D5603553

fbshipit-source-id: 3b0d878b9dfe50a49a8773b78a8de2e007f3299f

.travis.yml

@@ -33,7 +33,7 @@ before_script:
 
 # Build steps
 script:
-  - mkdir build && cd build && ${DEPS_DIR}/cmake/bin/cmake .. && make
+  - mkdir build && cd build && ${DEPS_DIR}/cmake/bin/cmake .. && make -j`grep -c processor /proc/cpuinfo`
 
 notifications:
   email:

BUILD.md

@@ -35,10 +35,12 @@ If you use `getdeps.sh`, then this should work out of the box.
 Build as follows:
 
 ```
-mkdir fboss/build
+mkdir fboss/build                         # start with a clean build dir
 cd fboss/build
-cmake ..
-make
+cmake ..                                  # build the Makefile
+NPROC=$(grep -c processor /proc/cpuinfo)  # lookup cores in system
+make "-j$NPROC"                           # spawn a thread per core
+
 ```
 
 FYI: the build status of open source fboss is tracked at: