ota: Validate any installed data's signature against our own

Try to prevent incompatible-signature system quirkiness

Change-Id: I73402d963a1b57ad0ee3c68ced4f2d7f074f927f
otasigcheck: set verification package to com.android.htmlviewer

We need to use something that will always be there and not replaced
by other packages.

Change-Id: Ide942865f284239ae2ae2503005ccc7e8272995c
otasigcheck: include multi-digit cert indices

If the cert index is greater than 9, we still want to include it.

Change-Id: I82787e59557ae0bb7f15da16630d2b0afb7cff06
otasigcheck: Fix the sed statement for multi-digit indices

It appears that some versions of sed do not work with the + symbol.
Instead of checking for one or more digits, check for a digit,
followed by zero or more digits.

Change-Id: I064df6a2bac4a634a3684ac1a5289dca1f4ba29c