How to reproduce:
1) Boot Ubuntu 14.04 64bit live
2) Open "disks"
3) Select 2 Hard drives and create a RAID 1 (mine had 2x 3TB SATA)
4) Once finished open Ubuntu installer
6) Click next and select the default settings (Erase everithing and install Ubuntu)
7) Once installation finshes in reports: grub-install /dev/md127p2 failed and propts you to select other partition. Which evere you select, the system will report that the installation is completed but once you reboot you will get boot disk failure, as if there is no Grub installation
ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: ubiquity 2.18.7
ProcVersionSignature: Ubuntu 3.13.0-24.46-generic 3.13.9
Uname: Linux 3.13.0-24-generic x86_64
ApportVersion: 2.14.1-0ubuntu3
Architecture: amd64
CasperVersion: 1.340
Date: Fri Jun 6 12:38:12 2014
InstallCmdLine: file=/cdrom/multiboot/ubuntu-14.04-desktop-amd64/preseed/ubuntu.seed boot=casper cdrom-detect/try-usb=true noprompt floppy.allowed_drive_mask=0 ignore_uuid live-media-path=/multiboot/ubuntu-14.04-desktop-amd64/casper/ initrd=/multiboot/ubuntu-14.04-desktop-amd64/casper/initrd.lz quiet splash --
LiveMediaBuild: It
ProcEnviron:
PATH=(custom, no user)
LANG=en_US.UTF-8
SHELL=/bin/bash
SourcePackage: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install)
According to your logs the subsequent attempts reported failure as well. This is because of a known bug in ubiquity that causes all subsequent attempts to fail after the first one has. Please try again and select the correct drive the first time, which would need to be your actual boot disk, i.e. /dev/sda.