release: Support r/o /usr/ports for cloudware

Set WRKDIRPREFIX=/tmp/ports DISTDIR=/tmp/distfiles when building tools
needed for uploading cloudware images.

While I'm here, adjust the bsdec2-image-upload build target to match
the style used by the Azure/GCE/Vagrant Makefiles.

MFC after: 3 days

releng-azure: Add ZFS support to Azure image buliding and uploading

Approved by: gjb (re)
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D41454

releng-azure: Use port name to install Azure CLI

To overcome package name changing on default Python version updates.

Approved by: gjb (re)
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D41453

Remove $FreeBSD$: one-line sh pattern

Remove /^\s*#[#!]?\s*\$FreeBSD\$.*$\n/

release: Remove unused variables in azure Makefile

Approved by: re (gjb)
Sponsored by: The FreeBSD Foundation

release: add _LOCATION to the list of required AZURE variables

Sponsored by: Rubicon Communications, LLC ("Netgate")

release: use tab-delimited variables in AZURE_UPLOAD_CONF

Sponsored by: Rubicon Communications, LLC ("Netgate")

Update Azure release bits

Imports the changes for building official images on Azure Marketplace,
which fulfill the requirements of Azure and FreeBSD cloud images like
disk layout and UEFI for Gen2 VM, along with some minor improvements like
configurations to speed up booting.

"CLOUDWARE" list will be updated after some more collaborations with re
completed.

Reviewed by: re (gjb)
Sponsored by: The FreeBSD Foundation
Technical assistance from: Microsoft
Differential Revision: https://reviews.freebsd.org/D23804

release: sprinkle UNAME_r hacks following c883b6fd8ccd

Pass UNAME_r override to make(1) for ports builds when building
ports for another branch.

MFC after: 3 days
MFC with: 0be274d37379, 80ab50e1de19, c883b6fd8ccd
Sponsored by: Rubicon Communications, LLC ("Netgate")

release: update to use git instead of svn:

Makefile.* (cloudware):
- Consistify setting the BUILDDATE for snapshots.

release.conf.sample/release.sh:
- Run 'git clone' in 'quiet' mode.

Makefile.inc1:
- Set BUILDDATE and export the variable.

Sponsored by: Rubicon Communications, LLC (netgate.com)

Remove the HH-MM suffix from the build date suffix.

It was useful when working out several kinks when
testing automated image uploading when retrying was
necessary, but now it is making things much too messy.

MFC after: 3 days
Sponsored by: The FreeBSD Foundation

Change the hour:minute delimiter from ':' to '-', since
the former is an invalid character in EC2 images.

MFC after: 3 days
Sponsored by: The FreeBSD Foundation

Consider PRERELEASE builds snapshots, in addition to CURRENT and
STABLE.

MFC after: 3 days
Sponsored by: The FreeBSD Foundation

Append the hour and minute to the snapshot suffix for EC2
AMIs and Azure VM images. This is particularly helpful for
testing to avoid name collisions, but also useful for cases
where a necessary rebuild is done before the date changes.

MFC after: 3 days
Sponsored by: The FreeBSD Foundation

Add Makefile.azure, used to upload VHD images to the
Microsoft Azure environment, similar to the EC2 AMIs.

MFC after: 3 days
Tested with: stable/10@r284517 (patched)
Sponsored by: The FreeBSD Foundation