Commit copies of bootstrap.ps1 for automated builds (#2458)

While this is copied by `launch.sh`, it needs to exist in
each folder for the automated Docker hub builds.

docker/.gitignore

@@ -1,3 +1,2 @@
 logs/**/*.log
 packages/
-nightly/*/bootstrap.ps1

docker/nightly/centos7/bootstrap.ps1

@@ -0,0 +1,8 @@
+# This is intended to be used inside Docker containers
+
+git clone --recursive https://github.com/$env:fork/PowerShell.git -b $env:branch
+Set-Location PowerShell
+Import-Module ./build.psm1
+Start-PSBootstrap -Package -NoSudo
+Start-PSBuild -Crossgen
+Start-PSPackage

docker/nightly/ubuntu14.04/bootstrap.ps1

@@ -0,0 +1,8 @@
+# This is intended to be used inside Docker containers
+
+git clone --recursive https://github.com/$env:fork/PowerShell.git -b $env:branch
+Set-Location PowerShell
+Import-Module ./build.psm1
+Start-PSBootstrap -Package -NoSudo
+Start-PSBuild -Crossgen
+Start-PSPackage

docker/nightly/ubuntu16.04/bootstrap.ps1

@@ -0,0 +1,8 @@
+# This is intended to be used inside Docker containers
+
+git clone --recursive https://github.com/$env:fork/PowerShell.git -b $env:branch
+Set-Location PowerShell
+Import-Module ./build.psm1
+Start-PSBootstrap -Package -NoSudo
+Start-PSBuild -Crossgen
+Start-PSPackage