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/_utility.ps1

@@ -0,0 +1,63 @@
+#
+# 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.
+#
+
+function header([string]$message)
+{
+    Write-Host -ForegroundColor Green "*** $message ***"
+}
+
+function info([string]$message)
+{
+    Write-Host -ForegroundColor Yellow "*** $message ***"
+}
+
+function error([string]$message)
+{
+    Write-Host -ForegroundColor Red "$message"
+}
+
+function setEnvIfDefault([string]$envVarName, [string]$value)
+{
+    If ([Environment]::GetEnvironmentVariable($envVarName) -eq $null)
+    {
+        [Environment]::SetEnvironmentVariable($envVarName, $value)
+    }
+}
+
+function setPathAndHomeIfDefault([string]$rootPath)
+{
+    If ($env:DOTNET_HOME -eq $null)
+    {
+        $env:DOTNET_HOME=$rootPath
+        $env:PATH="$rootPath\bin;$env:PATH"
+    }
+}
+
+function _([string]$command)
+{
+    & "$command"
+    if (!$?) {
+        error "Command Failed: '& $command'"
+        Exit 1
+    }
+}
+
+function _([string]$command, $arguments)
+{
+    & "$command" @arguments
+    if (!$?) {
+        error "Command Failed: '& $command'"
+        Exit 1
+    }
+}
+
+function _cmd([string]$command)
+{
+    cmd /c "$command"
+    if (!$?) {
+        error "Command Failed: 'cmd /c $command'"
+        Exit 1
+    }
+}