Clean up build scripts

Decompose into self-contained granular components
Provide reasonable defaults for cross cutting concerns, allowing for independent execution of steps
Start unifying Windows/Bash architecture

fix Bash CI scripts

dockerbuild.sh _common.sh path

Add missing restore-packages.sh

Copy/paste issues

Quote $SOURCE
fix .gitignore

PR Feedback

Merge in @SridarMS's work to avoid redownloading DNX

enabling build of dotnet-build

merge in @SridharMS's CentOS changes

Enable building FSC

enable restoring specific subdirectories

Fix dnx version check

Add missed dependency

Fix pathing to tests

Match Linux build version to Windows, fixing linux tests as a side effect.

workaround for coreclr#2215

fix pathing issue

disable building in docker

BUILD_IN_DOCKER was set, somehow...

fix headers

scripts/dev-dotnet.sh

@@ -10,7 +10,7 @@ SOURCE="${BASH_SOURCE[0]}"
 while [ -h "$SOURCE" ]; do # resolve $SOURCE until the file is no longer a symlink
   DIR="$( cd -P "$( dirname "$SOURCE" )" && pwd )"
   SOURCE="$(readlink "$SOURCE")"
-  [[ $SOURCE != /* ]] && SOURCE="$DIR/$SOURCE" # if $SOURCE was a relative symlink, we need to resolve it relative to the path where the symlink file was located
+  [[ "$SOURCE" != /* ]] && SOURCE="$DIR/$SOURCE" # if $SOURCE was a relative symlink, we need to resolve it relative to the path where the symlink file was located
 done
 DIR="$( cd -P "$( dirname "$SOURCE" )" && pwd )"
 REPOROOT="$( cd -P "$DIR/.." && pwd )"