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/common/_rid.sh

@@ -0,0 +1,37 @@
+#!/usr/bin/env bash
+#
+# Copyright (c) .NET Foundation and contributors. All rights reserved.
+# Licensed under the MIT license. See LICENSE file in the project root for full license information.
+#
+
+export UNAME=$(uname)
+
+if [ -z "$RID" ]; then
+    if [ "$UNAME" == "Darwin" ]; then
+        export OSNAME=osx
+        if [ -n "$(sw_vers -productVersion | grep 10.10.)" ]; then
+            export RID=osx.10.10-x64
+        elif [ -n "$(sw_vers -productVersion | grep 10.11.)" ]; then
+            export RID=osx.10.10-x64
+        else
+            error "unknown OS X: $(sw_vers -productVersion)" 1>&2
+        fi
+    elif [ "$UNAME" == "Linux" ]; then
+        # Detect Distro
+        if [ "$(cat /etc/*-release | grep -cim1 ubuntu)" -eq 1 ]; then
+            export OSNAME=ubuntu
+            export RID=ubuntu.14.04-x64
+        elif [ "$(cat /etc/*-release | grep -cim1 centos)" -eq 1 ]; then
+            export OSNAME=centos
+            export RID=centos.7.1-x64
+        else
+            error "unknown Linux Distro" 1>&2
+        fi
+    else
+        error "unknown OS: $UNAME" 1>&2
+    fi
+fi
+
+if [ -z "$RID" ]; then
+    exit 1
+fi