Fix KeyError when handling non-numbers in boot entries

[r0x0d]

The error happened because of the lack of a rule for the BootEntries parser,
before it only considered numbers between 0-9. However, the output of efibootmgr
can contain numbers and letters, for example, 000A is a valid output.

Jira reference: https://issues.redhat.com/browse/OAMG-6166
Bugzilla reference (If any): https://bugzilla.redhat.com/show_bug.cgi?id=2027686

[r0x0d]

Adding new entries to the efibootmgr

# /dev/vda1 is the name of the vagrant disk
efibootmgr -c -b 000A -d /dev/vda1 -p 1 -l "\EFI\centos\shimx64.efi" -L "CentOS 8"
efibootmgr -c -b 000B -d /dev/vda1 -p 1 -l "\EFI\centos\shimx64.efi" -L "CentOS 8"
efibootmgr -c -b 000C -d /dev/vda1 -p 1 -l "\EFI\centos\shimx64.efi" -L "CentOS 8"
efibootmgr -c -b 00A2 -d /dev/vda1 -p 1 -l "\EFI\centos\shimx64.efi" -L "CentOS 8"
efibootmgr -c -b A2A2 -d /dev/vda1 -p 1 -l "\EFI\centos\shimx64.efi" -L "CentOS 8"
...

Test outputs

First test output: 
BootEntries: {'0000': <convert2rhel.grub.EFIBootLoader object at 0x7f790a839978>,
 '0001': <convert2rhel.grub.EFIBootLoader object at 0x7f790a839828>,
 '0002': <convert2rhel.grub.EFIBootLoader object at 0x7f790a8392b0>,
 '0003': <convert2rhel.grub.EFIBootLoader object at 0x7f790a8397f0>,
 '0004': <convert2rhel.grub.EFIBootLoader object at 0x7f790a839710>,
 '0005': <convert2rhel.grub.EFIBootLoader object at 0x7f790a839470>,
 '0006': <convert2rhel.grub.EFIBootLoader object at 0x7f790a839588>,
 '0007': <convert2rhel.grub.EFIBootLoader object at 0x7f790a839358>,
 '0008': <convert2rhel.grub.EFIBootLoader object at 0x7f790a8391d0>,
 '0009': <convert2rhel.grub.EFIBootLoader object at 0x7f790a839dd8>,
 '000A': <convert2rhel.grub.EFIBootLoader object at 0x7f790a839eb8>,
 '000B': <convert2rhel.grub.EFIBootLoader object at 0x7f790a839fd0>,
 '000C': <convert2rhel.grub.EFIBootLoader object at 0x7f790a86b0f0>,
 '000D': <convert2rhel.grub.EFIBootLoader object at 0x7f790a86b1d0>,
 '000E': <convert2rhel.grub.EFIBootLoader object at 0x7f790a86b2b0>,
 '000F': <convert2rhel.grub.EFIBootLoader object at 0x7f790a86b390>,
 '0010': <convert2rhel.grub.EFIBootLoader object at 0x7f790a86b470>,
 '0011': <convert2rhel.grub.EFIBootLoader object at 0x7f790a86b550>,
 '0012': <convert2rhel.grub.EFIBootLoader object at 0x7f790a86b630>,
 '0013': <convert2rhel.grub.EFIBootLoader object at 0x7f790a86b710>,
 '0014': <convert2rhel.grub.EFIBootLoader object at 0x7f790a86b7f0>,
 '0015': <convert2rhel.grub.EFIBootLoader object at 0x7f790a86b8d0>,
 '0016': <convert2rhel.grub.EFIBootLoader object at 0x7f790a86b9b0>,
 '0017': <convert2rhel.grub.EFIBootLoader object at 0x7f790a86ba90>}
BootNum: 0017
BootOrder: ('0017', '0016', '0015', '0014', '0013', '0012', '0011', '0010', '000F', '000E', '000D', '000C', '000B', '000A', '0009', '0008', '0007', '0006', '0005', '0004', '0003', '0001', '0000', '0002')

Second test output:
BootEntries: {'0000': <convert2rhel.grub.EFIBootLoader object at 0x7fdda21879b0>,
 '0001': <convert2rhel.grub.EFIBootLoader object at 0x7fdda2187860>,
 '0002': <convert2rhel.grub.EFIBootLoader object at 0x7fdda21872e8>,
 '0003': <convert2rhel.grub.EFIBootLoader object at 0x7fdda2187828>,
 '000A': <convert2rhel.grub.EFIBootLoader object at 0x7fdda21873c8>,
 '000B': <convert2rhel.grub.EFIBootLoader object at 0x7fdda2187438>,
 '00A2': <convert2rhel.grub.EFIBootLoader object at 0x7fdda21874e0>,
 'A2A2': <convert2rhel.grub.EFIBootLoader object at 0x7fdda21875c0>,
 'AAA2': <convert2rhel.grub.EFIBootLoader object at 0x7fdda2187240>}
BootNum: A2A2
BootOrder: ('A2A2', 'AAA2', '00A2', '000A', '000B', '0003', '0001', '0000', '0002')

[abadger]

This looks like a good change to me. +1

[r0x0d]

Reviewd

[Venefilyn]

LGTM