EC2: Align partitions to 1 MB boundaries

Reviewed by:	jlduran, imp
MFC after:	2 months
Sponsored by:	Amazon
Differential Revision:	https://reviews.freebsd.org/D60455

release/tools/ec2.conf

@@ -20,6 +20,10 @@ export VMSIZE=8000m
 # and 4096 GB of RAM.
 export NOSWAP=YES
 
+# Align partitions to 1 MB boundaries; this is recommended by EC2 for
+# optimal EBS performance.
+export VM_PARTALIGN=1M
+
 ec2_common() {
 	if [ -z "${NO_ROOT}" ]; then
 		echo "ERROR: NO_ROOT not set" >&2