tests: matrix: add -sharestorage to test matrix
tests: matrix: add -sharestorage to test matrix

Currently fails like this:

=== RUN   TestRmwRace
doRead 0: corrupt block #0: cipher: message authentication failed
-wpanic turns this warning into a panic: doRead 0: corrupt block #0: cipher: message authentication failed
panic: -wpanic turns this warning into a panic: doRead 0: corrupt block #0: cipher: message authentication failed

goroutine 1293 [running]:
log.(*Logger).Panic(0xc00011c230, 0xc0003b17c8, 0x1, 0x1)
	log/log.go:224 +0xac
github.com/rfjakob/gocryptfs/internal/tlog.(*toggledLogger).Printf(0xc00007a780, 0x55a821a766a1, 0x20, 0xc0003b19f0, 0x3, 0x3)
	github.com/rfjakob/gocryptfs/internal/tlog/log.go:78 +0x1ef
github.com/rfjakob/gocryptfs/internal/fusefrontend.(*File).doRead(0xc0001ff420, 0x0, 0x0, 0x0, 0x0, 0x1000, 0x0, 0x1, 0xc000880000, 0x1020)
	github.com/rfjakob/gocryptfs/internal/fusefrontend/file.go:201 +0x8c9
github.com/rfjakob/gocryptfs/internal/fusefrontend.(*File).doWrite(0xc0001ff420, 0xc000248428, 0x10, 0x30, 0xff0, 0x3, 0x18)
	github.com/rfjakob/gocryptfs/internal/fusefrontend/file.go:291 +0xc9e
github.com/rfjakob/gocryptfs/internal/fusefrontend.(*File).Write(0xc0001ff420, 0x55a821b306a0, 0xc000fbde90, 0xc000248428, 0x10, 0x30, 0xff0, 0x7f4a00000000, 0x0)
	github.com/rfjakob/gocryptfs/internal/fusefrontend/file.go:378 +0x25e
github.com/hanwen/go-fuse/v2/fs.(*rawBridge).Write(0xc000168140, 0xc000096000, 0xc0002483d8, 0xc000248428, 0x10, 0x30, 0x55a821ad40e0)
	github.com/hanwen/go-fuse/v2@v2.0.4-0.20210125162859-8e0bbdb16cb7/fs/bridge.go:819 +0x26d
github.com/hanwen/go-fuse/v2/fuse.doWrite(0xc000170160, 0xc000248240)
	github.com/hanwen/go-fuse/v2@v2.0.4-0.20210125162859-8e0bbdb16cb7/fuse/opcode.go:191 +0x6f
github.com/hanwen/go-fuse/v2/fuse.(*Server).handleRequest(0xc000170160, 0xc000248240, 0xc000000000)
	github.com/hanwen/go-fuse/v2@v2.0.4-0.20210125162859-8e0bbdb16cb7/fuse/server.go:472 +0x2be
github.com/hanwen/go-fuse/v2/fuse.(*Server).loop(0xc000170160, 0xc000cd4101)
	github.com/hanwen/go-fuse/v2@v2.0.4-0.20210125162859-8e0bbdb16cb7/fuse/server.go:445 +0x198
created by github.com/hanwen/go-fuse/v2/fuse.(*Server).readRequest
	github.com/hanwen/go-fuse/v2@v2.0.4-0.20210125162859-8e0bbdb16cb7/fuse/server.go:312 +0x41d
    matrix_test.go:354: Write failed

rfjakob/gocryptfs,rfjakob/gocryptfs,rfjakob/gocryptfs,rfjakob/gocryptfs